1. Field of the Invention
The present invention relates to an endoscope apparatus capable of controlling various imaging modes and a control method therefor.
2. Description of the Related Art
Endoscope apparatuses for obtaining an image of a body cavity, such as esophagus, stomach, large intestine, and the like, by inserting a scope inside of the body cavity are used in order to perform image diagnosis for the state of the body cavity. Recently, when performing image diagnosis through the endoscope, it has become possible that an endoscope image obtained by the scope is displayed on a monitor in real time and the doctor is able to perform image diagnosis while confirming the imaged area with the monitor.
In order to facilitate image diagnosis, various observation modes using the endoscope are available, including ordinary observation mode in which a subject illuminated with white light is observed, fluorescence observation mode in which fluorescence emitted from a subject when illuminated with excitation light is observed, narrowband mode in which a subject illuminated with narrowband light is observed, and the like.
Here, in order to assist a doctor in performing image diagnosis efficiently, a method for automatically switching these modes is proposed as described, for example, in Japanese Unexamined Patent Publication No. 2007-020728. Japanese Unexamined Patent Publication No. 2007-020728 proposes an automatic switching method among the ordinary observation mode, narrowband observation mode and fluorescence observation mode described above according to the magnification of the lens.
A method for automatically changing the magnification of the imaging lens attached to the tip of the scope according to the imaging mode is also proposed as described, for example, in U.S. Pat. No. 6,582,362. More specifically, U.S. Pat. No. 6,582,362 proposes a method that, based on the fact that, under AEC (auto exposure control) for controlling the aperture of the light source unit to keep the brightness of an image constant, if the distance to the object is changed, the aperture is also changed, determines if it is near view imaging or distant view imaging by figuring out the distance to the object from the state of the aperture and performs high frequency component enhancement processing if the image is an image obtained by near view imaging or low frequency enhancement processing if the image is an image obtained by distant view imaging.
In addition to the method for measuring the distance between the scope and subject using AEC as described in U.S. Pat. No. 6,582,362, there is a demand for a method that enables efficient image diagnosis by automatically switching between near view imaging and distant view imaging according to the imaging region.
Therefore, it is an object of the present invention to provide an endoscope apparatus capable of automatically switching imaging modes according to the type of a subject, and a control method therefor.
As for the narrowband observation mode, for example, Japanese Unexamined Patent Publication No. 2002-095635 proposes an apparatus that emits narrowband light to a living tissue using a narrowband filter to obtain a narrowband image that allows a high contrast observation of a blood vessel or the like on a surface layer of a mucous membrane and displays the narrowband image.
In the mean time, Japanese Unexamined Patent Publication No. 2003-093336 proposes an apparatus that performs a matrix operation on a color image signal obtained with a wide wavelength range without using an optical narrowband filter to obtain a spectrally estimated image which is equivalent to that obtainable using the narrowband filter and displays the spectrally estimated image.
The narrowband image obtained by the apparatus described in Japanese Unexamined Patent Publication No. 2002-095635, however, is an image obtained by emitting light transmitted through the narrowband filter, thus causing a disadvantage that the amount of light emitted to a living tissue is insufficient and the image becomes dark. This disadvantage particularly becomes significant when a distant view image is obtained. In the mean time, the spectrally estimated image obtained by the apparatus described in Japanese Unexamined Patent Publication No. 2003-093336 has sufficient brightness, but the wavelength estimation by the matrix operation has limitations on the accuracy, whereby the image quality may be degraded compared to the narrowband image. This disadvantage becomes more significant when a near view enlarged image is obtained.
In view of the circumstances described above, it is a further object of the present invention to provide an image obtaining method and an endoscope apparatus capable of obtaining an appropriate image in both distant view imaging and near view enlargement imaging.